1. Field of the Invention
The present invention relates to a laser converging apparatus, an optical pickup device, and an optical disk recording/reproducing apparatus.
2. Description of the Related Art
An optical pickup device has been in popular use, which device includes a semiconductor laser that emits laser light of different wavelengths (780 to 790 nm for CD; 650 to 660 nm for DVD) onto optical disk media having different protective layer thicknesses, such as a CD (Compact Disc) with a protective layer of 1.2 mm thick and a DVD (Digital Versatile Disc) with a protective layer of 0.6 mm thick, and an objective lens usable for both optical disk media. This optical pickup device corrects a spherical aberration caused by the difference between the protective layer thicknesses, utilizing the difference between the wavelengths, to enable recording and reproduction on each optical disk medium.
These days, however, newly proposed optical disk media have emerged. These media have respective different protective layer thicknesses, such as a Blu-ray Disc (registered trademark) with a protective layer of 0.075 to 0.1 mm thick and an HD DVD (High Definition DVD) with a protective layer of 0.6 mm thick, and are capable of recording operation at higher density than CDs or DVDs. For the Blu-ray Disc, such an optical pickup device is used that it includes a semiconductor laser that emits blue-violet laser light having a wavelength of 400 to 410 nm and an objective lens having a numerical aperture (hereinafter referred to as NA) of 0.85. For the HD DVD, such an optical pickup device is used that it includes a semiconductor laser that emits the blue-violet laser light having the same wavelength as that for the Blu-ray Disc and an objective lens having an NA of 0.65. Individual optical pickup devices, therefore, are employed for the Blu-ray Disc and HD DVD, respectively.
These conventional optical pickup devices are, for example, disclosed in JP-A No. 14-184026 and described on page 115 of DVD Textbook by Haruki Tokumaru, Fumihiko Yokokawa, and Mitsuru Irie.
Recoding and reproducing on both Blu-ray Disc and HD DVD, however, requires individual pickup devices compatible respectively with the Blu-ray Disc and HD DVD. This raises a problem of higher cost, larger size, and heavier weight of pickup devices. The same problem happens in an optical disk recording/reproducing apparatus into which the optical pickup devices are incorporated. Besides, applying the blue-violet laser light of the same wavelengths to Blu-ray Disc and HD DVD makes impossible the employment of the conventional method utilizing the differences between wavelengths, thus makes difficult manufacturing of an optical pickup device that can be used for both Blu-ray Disc and HD DVD.